In recent years with development of three-dimensional fine processing techniques, the systems attracting attention are those which comprise fluid elements such as a fine flow path, a pump, and a valve, and a sensor integrated on a substrate like glass or silicon, and conduct chemical analysis on the substrate. Such a system is called a microanalysis system, a μ-TAS (Micro Total Analysis System), or Lab on a Chip. The miniaturization of the chemical analysis system enables decrease of an ineffective space volume and remarkable decrease of the sample size.
The miniaturization enables also shortening of the analysis time and decrease of power consumption of the entire system. Further, the miniaturization is promising for lowering the price of the system. Furthermore, the μ-TAS is promising in medical services such as home medial care and bed-side monitoring, and biological chemical techniques such as geonomics analysis and proteomics analysis.
Japanese Patent Application Laid-Open No. 10-337173 discloses a micro-reactor for conducting a sequence of biochemical experiment steps comprising mixing solutions to cause reaction, analyzing quantitatively the reaction product, and separating the product, by using combination of cells. FIG. 17 illustrates schematically a concept of micro-reactor 501. Micro-reactor 501 has an isolated reaction chamber closed tightly with a flat plate on a silicon substrate. This micro-reactor has reservoir cell 502, mixing cell 503, reaction cell 504, detection cell 505, and separation cell 506 in combination. By providing such a reactor in plurality on a substrate, many biochemical reactions can be allowed to proceed simultaneously concurrently. Not only the analysis, but material synthesis such as protein synthesis can be conducted in the cells.
Japanese Patent Application Laid-Open No. 5-1669 discloses a valve employing a diaphragm, and a micro-pump utilizing the valve and a piezo element.
U.S. Pat. No. 6,533,400 discloses an ink-jet head employing a valve constituted of a movable member (cantilever).
Jr-Hung Tasai and Liwei Lin: “A Thermal Bubble Actuated Micro Nozzle-Diffuser Pump”, Proceedings of the 14th, IEEE International Conference on Micro Electro Mechanical Systems, 2001, pp. 409-412 discloses a valveless micro-pump utilizing a liquid-control function of a bubble generated by heating of the liquid and a nozzle type diffusion element.
Jong Soo Ko, et al.: Appl. Phys. Lett. Vol. 81, No. 3, Jul. 15, 2002, pp. 547-549 discloses an optical switch employing an actuator utilizing interaction of a magnetic field and an electric current.
Jin Qiu, et al.: “Proceedings of MEMS 2001”, 2001, pp. 353-356 mentions usefulness of mechanical bistability for relays and valves.
However, conventional micro-valves employing a diaphragm or a cantilever require external force to keep the valve opened or closed as desired.
On the other hand, the mechanically bistable element needs extra driving force for transformation between the two stable structures owing to a high potential energy barrier between the two structures in comparison with an element having no mechanical bistability.
Generally the lower potential energy barrier between the two structures for decreasing the aforementioned extra driving force will make instable the retention of the stable states.